Tupelo, Mississippi (CNN) -- A Tupelo, Mississippi, man has been charged with possession and use of a biological agent as a weapon in connection with an investigation into ricin-tainted letters sent to President Barack Obama and others, federal authorities said Saturday.

The federal charges against James Everett Dutschke come two days after prosecutors dropped charges against Paul Kevin Curtis in the same case amid Curtis' claims he was framed.

Dutschke, 41, is expected to appear in U.S. District Court in Oxford on Monday before Magistrate Judge S. Allan Alexander, according to a statement released by the U.S. attorney in the Northern District of Mississippi.

Dutschke was arrested at his home early Saturday without incident, FBI spokeswoman Deborah Madden said. Earlier this week, agents searched Dutschke's residence and former martial arts studio, though it's not clear what they found.

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The arrest of Dutschke is the latest twist in a case that began last week when federal authorities said letters containing ricin, a deadly toxin, were sent to Obama, a Mississippi senator and a local judge.

On Tuesday, prosecutors dropped charges against Curtis of Corinth, Mississippi, who was arrested April 17 in connection with the letters.

At a court hearing the day before the charges were dropped, Curtis said he was being framed and identified Dutschke as a potential culprit.

The letters -- sent to Obama; Sen. Roger Wicker, R-Mississippi; and Sadie Holland, a judge in Lee County, Mississippi -- touched off anxieties in Washington and elsewhere in the wake of the bombs at the Boston Marathon. The two incidents were unconnected, officials said.

The FBI said the letters tested positive for ricin, a toxin derived from castor beans that has no known antidote. No illnesses have been reported.

The letters read, in part: "To see a wrong and not expose it, is to become a silent partner to its continuance."

They were signed "I am KC and I approve this message," a source told CNN.

Each letter had a Memphis, Tennessee, postmark and no return address.

Dutschke's attorney, Lori Basham, has said her client used to work for Curtis' brother, but the two have had no contact since 2010. Basham declined to comment on Dutschke's arrest Saturday.

Curtis said Wednesday that he didn't even know what ricin was until he got out of jail and looked it up on the Internet.

When police suddenly stormed his home last week, Curtis said an investigator asked him about ricin, and Curtis said he responded, "Well, I don't eat rice, and I don't have any rice in the house."

Asked about the arrest Saturday, a White House official told CNN that Obama has been kept abreast of developments throughout the ordeal.

Vivian Kuo reported from Tupelo, Mississippi; Chelsea J. Carter reported and wrote from Atlanta. CNN's John Branch and William Mears contributed to this report.

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